In some applications, it is advantageous, or necessitated, to capture images in a motion-synchronized manner. For example, in so-called TDI methods, that is, methods for a time-delayed integration, an object is shifted with respect to an image sensor. If the mapping of an object moves with respect to the image sensor, it is often desirable to capture the moving object almost free of distortion.
CMOS image sensors for the capture of images are already known from the art, scientific literature and different patent documents.
In contrast, methods for time-delayed integration (i.e. TDI methods) up to date have been realized almost exclusively with CCD sensors (i.e. sensors with a charge-coupled means). They have some inherent disadvantages. For example, by the bucket-brigade method, charges are lost with every shift clock, which is also called smearing. For example, with a high object speed, or a large mapping scale, an object quickly sweeps over several rows, perhaps all rows of a sensor matrix. Accordingly, with an accumulation across many rows, many shift operations are to be performed. Thus, an important part of the photo charges is lost by smearing, whereby an advantage by accumulation is strongly leveled. For this reason, there are only very few manufacturers offering TDI CCD sensors, such as Fairchild and Hamamatsu. These manufacturers have special processes at their disposal, by which the smear rate is reduced with a high effort in the technical process. Accordingly, the sensors are high-priced. Currently, multi-row or area sensors with several thousand pixels cost approximately between $2.000 and $5.000 a piece.
For this reason, in some cases, high-speed CMOS/CCD sensors with an accumulation are alternatively employed in camera systems. This concept also shows significant disadvantages. For example, due to a fast readout, only a very short exposure time is available. Likewise, single-shot signals are noised due to the high readout bandwidth.